Manufacturers in the semiconductor-technology field are continually looking to produce electronic devices that are increasingly smaller and increasingly quicker, having electronic-element densities that are as high as possible.
A well-known technique for producing patterns on a semiconductor substrate consists in using a photolithographic technique. In this technique a pattern, such as an array of parallel lines, is produced on the substrate by depositing a film of material on the substrate, creating via photolithography a resist mask comprising openings corresponding to a pattern complementary to the pattern to be produced, then etching the material through the mask and removing the resist.
An optional subsequent step of transfer into the substrate consists in etching the substrate using the pattern produced as a hard mask.
However, this optical photolithography method is limited by the wavelength of the light source used to expose the resist. Currently lines having a width of 45 nm or less cannot be produced using optical lithography.
Thus another technique has been proposed called SIT (sidewall image transfer) by those skilled in the art. Production of interleaved patterns according to this technique is described in FIGS. 1a to 1f. In a first step illustrated in FIG. 1a, lines are produced in a material A using photolithography and etching. Then, in a second step, illustrated in FIG. 1b, a spacer is formed in a material B around each line of the material A. Next, in a third step illustrated in FIG. 1c, the material A is removed by selective etching, there remaining then only the spacers made of material B. In a fourth step illustrated in FIG. 1d, another photolithography step is carried out with a resist mask so as to remove, in a subsequent step illustrated in FIG. 1e, the ends of the spacers made of material B, and thus obtain, at the end of a final step of removing the resist, illustrated in FIG. 1f, a succession of lines made of material B separated by a gap twice as small as the lines, initially obtained by photolithography, made of material A.
However, this method requires two photolithography steps.